The present invention relates to cable television communication networks and, in particular, to optimizing upstream transmissions in such networks.
Cable networks, sometimes referred to as CATV (community antenna TV) networks, serving residential and business premises not only provide a medium for the delivery of audio and video traffic (e.g. television and radio) for which these networks were originally designed but also provide a medium for the delivery of new services such as telephony, Internet, multimedia and data services. The new services can provide the cable system provider with an additional source of revenue.
Originally, many cable networks were designed to carry audio and video traffic (e.g. television and radio) only downstream from a cable system provider to cable subscribers. Today, many of the new services, such as telephony, require the cable network not only to carry traffic downstream from the cable system provider to the cable subscribers (downstream traffic) but also to carry traffic upstream from the cable subscribers to the cable system provider (upstream traffic). However, as shown in FIG. 1, conventional cable networks are typically implemented as a large analog bus, with analog amplifiers located along coaxial cable to boost signals where required. Since all upstream traffic typically accumulates at a single receiver point at the cable system provider, typically called the system head end, a particular problem that has been experienced is the cumulative effect of amplifier generated noise and signal distortion from the analog amplifiers on the upstream traffic. Moreover, another problem that has been experienced with the upstream traffic is the cumulative effect of ingress noise appearing at the system head end from spurious sources such as noise from cable subscriber equipment. A catastrophic ingress of noise from even a single cable subscriber can prevent any reliable upstream traffic from other cable subscribers. It is typically very difficult for a cable network provider to reduce ingress noise introduced from cable subscribers since the ingress noise is often introduced somewhere inside the premises of the cable subscribers. Other sources of ingress noise include noise from amateur radio (HAM) operators operating near the cable (CATV) network. Noise from amateur radio operators typically enters the cable (CATV) network at a point or points in the coaxial cable where the shield of the coaxial cable has been compromised. The cumulative effect of the amplifier generated noise and signal distortion and the ingress noise limits the capacity and reliability of the cable (CATV) network to carry upstream traffic.
To,minimize the problems identified above, persons skilled in the art have used hybrid fibre-coax (HFC) architectures for cable networks. Fibre optic cable is used on a trunk from a system head end to various fibre nodes. Coaxial cable is connected from the fibre nodes to a plurality of cable subscribers. Analog amplifiers are used on the coaxial cable to boost the downstream traffic and the upstream traffic. The analog amplifiers often introduce amplifier generated noise and signal distortion on the upstream traffic and the downstream traffic. The amplifier generated noise and signal distortion and any ingress noise from spurious sources (typically from the cable subscribers) all converge and accumulate at the respective fibre node. Finally, all the amplifier generated noise and signal distortion introduced by the analog amplifiers and all the ingress noise converge and accumulate at the system head end (along with all the upstream traffic).
With a hybrid fibre-coax (HFC) architecture, very little ingress noise is picked up by the trunks. However, since much of the ingress noise originates at or near the cable subscribers, much of the ingress noise is not fundamentally reduced as compared with a conventional cable network using only coaxial cable, although improvements are realized since all the amplifier generated noise and signal distortion from the analog amplifiers and the ingress noise is divided over multiple fibre nodes. The cumulative effect of the amplifier generated noise and signal distortion and the ingress noise on the system head end limits the reliability and capacity of the conventional cable network using the hybrid fibre-coax (HFC) architecture to carry upstream traffic.
In order to minimize the problems identified above, persons skilled in the art have proposed that the upstream traffic be sent using digital signals and that digital regenerators be used typically at each analog amplifier stage. The digital regenerators regenerate the digital signals and help clean out noise. The use of digital regenerators allow for much higher transmission capacity and reliability. PCT patent publication WO97/01906, published on Jan. 16, 1997, discloses the use of digital regenerators to regenerate and reduce noise on upstream traffic carried outside the recommended bandwidth of coaxial cable used in a conventional cable network. Persons skilled in the art have also attempted to address the above noted problems by using relatively costly, noise immune modulation techniques on the upstream traffic e.g. Code Division Multiplex Access (CDMA) techniques.
It is an object of the present invention to provide an improved hybrid amplifier and regenerator (HAR) device, an improved digital regenerator, an improved communication network, a method for carrying downstream traffic and upstream traffic in a communications network, and a method for processing digital upstream traffic in a digital regenerator in which the above mentioned problems are obviated or mitigated.
In accordance with one aspect of the present invention there is provided a hybrid amplifier and regenerator (HAR) device for use in a communications network for carrying downstream traffic in a forward frequency band and for carrying digital upstream traffic in a reverse frequency band spaced from the forward frequency band. The hybrid amplifier and regenerator (HAR) device comprises an analog amplifier for amplifying the downstream traffic and a digital regenerator. The digital regenerator comprises mapping circuitry for mapping digital upstream traffic carried in at least one ramp band which is part of the reverse frequency band to digital upstream traffic carried in at least one express band which is also part of the reverse frequency band but spaced from the at least one ramp band, and an express band transmitter for transmitting digital upstream traffic from the mapping circuitry in the at least one express band.
In accordance with another aspect of the present invention there is provided a digital regenerator for use in a hybrid amplifier and regenerator (HAR) device. The digital regenerator comprises mapping circuitry for mapping digital upstream traffic carried in at least one ramp band which is part of the reverse band to digital upstream traffic carried in at least one express band which is also part of the reverse band but spaced from the at least one ramp band, and an express band transmitter for transmitting digital upstream traffic from the mapping circuitry in the at least one express band.
In accordance with another aspect of the present invention there is provided a communications network for carrying downstream traffic from a system head end to a plurality of cable subscribers within a forward frequency band, and for carrying digital upstream traffic from the plurality of cable subscribers to the system head end in a reverse frequency band which is spaced from the forward frequency band. The communications network comprises transmission means for interconnecting the system head end and the plurality of cable subscribers. The communications network further comprises a plurality of hybrid amplifier and regenerator (HAR) devices located at spaced intervals along the transmission means. Each hybrid amplifier and regenerator (HAR) device comprises amplification circuitry for amplifying said downstream traffic and a digital regenerator. Thee digital regenerator comprises mapping circuitry for mapping digital upstream traffic carried in at least one ramp band which is part of the reverse frequency band to digital upstream traffic carried in at least one express band which is also part of the reverse frequency band but spaced from the at least one ramp band, and an express band transmitter for transmitting digital upstream traffic from the mapping circuitry in the at least one express band. The communications network further comprises cable modems for receiving the downstream traffic for the cable subscribers and for sending the digital upstream traffic from the cable subscribers in the ramp bands.
In accordance with another aspect of the present invention there is provided a method for carrying in a communications network downstream traffic in a forward frequency band and digital upstream traffic in a reverse frequency band which is spaced from the forward frequency band. The method comprises amplifying and transmitting said downstream traffic in the forward frequency band, mapping digital upstream traffic carried in at least one ramp band which is part of the reverse frequency band to digital upstream traffic carried in at least one express bands which is also part of the reverse frequency band but spaced from the at least one ramp band, and transmitting digital upstream traffic in the at least one express band.
In accordance with another aspect of the present invention there is provided a method for processing digital upstream traffic in a digital regenerator. The method comprises mapping digital upstream traffic carried in at least one ramp band which is part of the reverse frequency band to digital upstream traffic carried in at least one express band which is also part of the reverse frequency band but spaced from the at least one ramp band, and transmitting digital upstream traffic in the at least one express band.
In accordance with another aspect of the present invention there is provided a hybrid amplifier and regenerator (HAR) device for use in a communications network for carrying downstream traffic in a forward frequency band and for carrying digital upstream traffic in a reverse frequency band spaced from the forward frequency band. The hybrid amplifier and regenerator (HAR) device comprises an analog amplifier for amplifying said downstream traffic, and a digital regenerator. The digital regenerator comprises mapping circuitry for mapping digital upstream traffic carried in a ramp band which is part of the reverse frequency band to a plurality of virtual channels carried in an express band which is also part of the reverse frequency band but spaced from the ramp band, and an express band transmitter for transmitting the virtual channels from the mapping circuitry in the express band.
In accordance with another aspect of the present invention there is provided a hybrid amplifier and regenerator (HAR) device for use in a communications network for carrying downstream traffic in a forward frequency band and for carrying digital upstream traffic in a reverse frequency band spaced from the forward frequency band. The hybrid amplifier and regenerator. (HAR) device comprises an analog amplifier for amplifying said downstream traffic, and a digital regenerator. The digital regenerator comprises mapping circuitry for mapping digital upstream traffic carried in a plurality of virtual channels in an express band which is part of the reverse frequency band to a single virtual channel in the express band, and an express band transmitter for transmitting the single virtual channel from the mapping circuitry in the express band.
In accordance with another aspect of the present invention there is provided a digital regenerator for use in a hybrid amplifier and regenerator (HAR) device. The digital regenerator comprises mapping circuitry for mapping digital upstream traffic carried in a ramp band which is part of the reverse frequency band to a plurality of virtual channels carried in an express band which is also part of the reverse frequency band but spaced from the ramp band, and an express band transmitter for transmitting the virtual channels from the mapping circuitry in the express band.
In accordance with another aspect of the present invention there is provided a digital regenerator for use in a hybrid amplifier and regenerator (HAR) device. The digital regenerator comprises mapping circuitry for mapping digital upstream traffic carried in a plurality of virtual channels in an express band which is part of the reverse frequency band to a single virtual channel in the express band, and an express band transmitter for transmitting the single virtual channel from the mapping circuitry in the express band.
In accordance with another aspect of the present invention there is provided a method for multiplexing a plurality of express band transmissions, each express band transmission having a duration, from a plurality of respective downstream hybrid amplifier and regenerator (HAR) devices at an upstream hybrid amplifier and regenerator (HAR) device in the communications network. The method comprises determining a start time for each express band transmission which ensures that the express band transmissions will arrive at the upstream hybrid amplifier and regenerator (HAR) device without interfering with each other; and, beginning each express band transmission from each respective downstream hybrid amplifier and regenerator (HAR) device at each respective start time.